Helicoidal body and cutter for gear-wheels.



W. F. ZIMMERMANN.

' HELICOIDAL BODY AND CUTTER FOR GEAR WHEELS.

APPLICATION FILED APR. 5. 1913.

1,151,324.. f PfIIenIedAug. 24,1915;

4 .SHEETS-SHEET 3- W'. F. ZIMMERMANN. 4 HELIQOIDALgBOD'Y AND )UTTERAFOR- GEAR WHEELS..

. APPL| c ^T|oN man APR. 5. v1913. 1,151,324. mntea Aug. 2 4,- 19155 y 4 SHEETS-SHEET 4.

Ffa f4 fil I UNITED siArEsA PATENT?- oEEIoE. i

WILLIAM E. ZIMMERMANN, or NEWARK, NEW JERSEY, AssIGNoE To .GouLD & EBERHARDT, o E NEWAEK, NEW JERSEY, A CORPORATION E NEW JERSEY.

IIELIcoIDAL BODY AND GUTTER' Eon GEAE;WI'IEELs.

To all whomit may concern.' .A

Be it known-that I, WILLIAM F. ZIMMER MANN, a citizen kof the United States, and -a resident of Newark, in' the county of Essex and State of New Jersey, have invented certainA new andA useful Improvements in Helicoidal Bodies and Cutters for Gear- IVheels, and do hereby declare the following specification, taken in connection with the drawings forming part of same, to bea full,

clear, concise, and exact description ofthe principle, invention, and the best mode contemplated toapply said principle, soas to distinguish it from other inventions and enable any person skilled in the art to which it appertains or with which it is most nearly connected to make, construct, and use the same@ j IThis invention relates primarily to a helicoid adapted to be used in connection with gearing and more particularly to a helicoidal cutter and a method to generate correctly,

the tooth forms of gear wheels.

l The primary object of this invention is to provide al helicoid which is so formed that when used withgear wheels, the'projection of the various points of the helicoidal surfaces, on a plane perpendicular to'a chordal plane, will envelop the basic form ofthe involute system ofgear teeth.

A helicoid so formed and provided with cutting teeth in the usual manner and known as a hob or rotary generating cutter is adapted to generate correctly the toothforms of particular forms.

The novelty of this invention will be readinvolute gear teeth.

The i annexed drawings and description thereof set forth in detail certain mechanical forms which embody 'the principles of this invention. It is, however, to bev understood that thisinvent-ion is not limited to these Specification of Letters Patent. Application filed April 5, 1913. Serial o. r(59,110.

vention.

tool. l

Patented Aug'-2g4, 1915.

and 5 illustrate a methodof producing the helicoid shown in Fig. 2. Figs. Q6 and 7 show a helicoidal cutter embodying the in- Fig. 8 shows a plan view of a modified helicoidal cutter in connectionwith a gear 4wheel illustrating the method of cor- .rectly forming the teeth of gear Wheels by 'a rotary generating cutter. Fig. 9 is a front elevation of Fig. 8. Fig. 10 -is a diagram showing the position of the various planes.

Helicoids as shown in Fig. 1 are generally used for worms or helicoidal cutter blanks, and are formed so thatfasection thereof in -a diametral plane envelops the basic form of the involute system of vgear teeth. The usual method employed to form a helicoid is to uniformly move the tool, provided with the basic involute form, in the direction of the helicoidal axis and simultaneously imparting an angular o r rotary motion to said helicoid relative to the axial travel of the The surfaces of a helicoid formed as just I described, when projected on a plane perpendicular to a chordal plane a w, of Fig. 1, will not envelop the basicv or' true rack form conjugate to thev form of tooth of a gear meshing with such helicoid or worm. Such basic form is only found in a plane X X, passing through the axis of the helicoid. i

In Fig. 1 of the drawings the dotted lines 1 and 2 show the form of the helicoidal teeth in a plane passing through theaxis as at X X,. These lines 1 and 2 also show the contour of the tool used to produce the heli coid. The full lines 3 and 4 show the form enveloped by vprojecting the various points of the helicoidal surfaces, on a plane perpendicularto the chordal plane a a,

The helicoidin Fig. 2 is made so that the full lines 5 and 6 envelop the basic form of the involute system of gear teeth and the dotted lines 7 and 8 represent Athe form o'f the tool-used or a section in a through the axis Y Yr.

By referringtoFig. 3. a comparison is shown between the axial sections of Figs. 1 and 2. The dotted lines 9 and 10 represent an axial section of Fig. l and the full lines 11 and 12 show a similar section of Fig. 2. The dotted lines 9 and 10 envelop the same shape as .the full linres 5v and 6 of Fig. 2

plane passing which shape is substantially the baffo form Aof the involute system of gear teeth.

Upon inspection ofY Fig. 3 it will be seen that the section shown by the full lines 11 and l2, representing an axial section of Fig. f2 is smaller in area than the dotted line-section representing the axial section of Fig. 1. lf`urther1nore5'it is obvious that the included angle of the full lines 11 and 12 is less than that of the dotted lines 9 and 10.

The form of the tool to produce. the helieoidvof F ig. 2 represented by the dotted lines 7 and S. is obtained by a process similar to that shown in Figs. l and 5 now to be explained.v The helicoid shown inl Fig. l is similar to that commonly used as a worin and issubstantially the 'same as shown in Fig. l. The numerals I, II and III represent different positions of the saine tool. After the helicoid is formed in the usual manner, as hereinbefore described, by a tool placed in the position II as shown in Figs-l and 5, said tool is moved downward in a straight line from said position II to that at I, as shown in Fig. 5. The tool is then given the usual movement parallel to the axis Z Z, of the helicoid in the direction of the arrow in Fig. el. After each passage. of the tool from right to left in F ig. l, it is raised in a straight line in the direction of the arrow in Fig. 5, or in other words,the tool is given .a chordal feed', along the chord b, until it reaches the position 1H. vhen the tool is below that. of position II it cuts from the helicoid the portion 13, which is shown continued.

partly around the helicoid by the dot and dash lines lland 15. After the tool leaves position II and advances to position III it cuts the portion 1G from the helicoid, which is also shown continued partly around the helicoid by dot and dash lines 17 and 18. The dot and dash lines 11' and 17 resulting from the combined transverse and chordal travel of the tool are the same as the full lines 5 and G of Fig. 2 and an axial section of the helicoid so modified would therefore be the same as that shown by the dotted lines 7 and S of Fig. 2, and determines the shape of the tool to produce a modifiedhelicoid without the chordal feed. The proper width and angles of the tool to produce the modified helicoid of Fig. can also be determined by descriptive geometry by plotting a series of intersections of the tool along the chord of 7) 7), with the helicoid. to determine the eii'ect of the chordal` feed. -The helicoidal cutter illustrated by Figs. 6 and 7 is made by providing a helicoid similar to that of (Fig. 2 with flutes or grooves 19 and properly relieving the sides 20 and Q1 to give the correct amount of clearance. `The dotted lines 22 and 23 represent the projection of the points on the helicoidal surface of the cutter on a plane perpendicular to the chordal plane, and envelop substantially the same form as the full illustrated'by Figs. 8 and 9. By inspection' of said drawings it will be noted that the 'axis C C, of the'helicoidal cutter'is at right angles tothe gear axis (l rl, and not at a slight angle thereto, equivalent to the angularity of the helicoid. i

It has been the practice heretofore to set the cutter axis at an angle with the gear axis, equivalent to the angle of the helicoid. The difficulty with this, however, is in the fact that a true involute section is not presented to the face of the gear to be cut. The section brought at right angles to the axis of the gear by angularly adjusting the cutter, has the form of a part ofi an ellipse and not the straight line, necessary for the basic involute form. This fact is readily apparent when it is considered that a plane cut ting a cylinder at an angle with the axis other than at right angles, willcut from said cylinder an elliptic section.

ln Fig. S the dotted lines 21 and :25 represent the chordal projection of the helicoidal surfaces'and the lines 2G and 2i' represent the modified teeth of the -helicoidal cutter which are substantially the same as the full line. section 11 and 12 of Fig. 3.

The helicoidal` cutter and gear blank are rotated in unison and are fed relatively to each other .substantially parallel with the axis (l (1 of the gear blank. The 4forming of the gear tooth curve is accolnplished by the movement of the, helicoidal teeth along the axis c c, of the cutter as it is rotated. Figs. S and 9 represent a gear being recut with a finishing cutter to more clearly show the action of formation.

The curve 2S is formed bythe sides :29 ofthe cutting teeth when they are below the center line c c, of Fig. 9, best seen at 30. The curve Slis generated by the sides 32 of the cutting teeth when they are above the center line c c, of Fig. 9, best seen at 33. The lines 30 and 33 are straight and at right angles to the axis of the gear wheel and follow out the curve of the tooth from its two extremes. Y

face of they .gear will eliminate the line'l33 and all of the gear tooth forms'will be cc'ymf Pleted. a

y' The action-which takes place in forming .thegear toothlcurves, can also readily be' seen` from Figsl-fzliand 5 by assuming that i -the`h'elicoidis the cutting or forming tool,

usdto form the rack tooth -shown at I and II with the portions 13 and 16 respectively removed. From these drawings it is manifest that the portion 13 is removedI vvhile the rack tooth is below. the center 'Z Z, and

theflportion 16 is removed when said tooth is above said center Z Z and practically nothing is removed. as lthe tooth passes across the' center of the helicoid',

. Gear tooth Acurves formed as heretofore by angularly adjusting the axis of the helicoidal cutter had the disadvantage, not vonly of the elliptic section as hereinbefore described, but also that the flutes 19 (Fig: 7

had to be in a helical line necessarily nor-A` l -Imal to -the.teeth This produced unsymmetric teeth so that when the two curves of two gears formed by opposite'sides of the cutterl were rolled together they did not havethe proper rolling action but showed interferences. Now, with the process shown .36 in Figs. 8 and 9 the helicoidal cutter. is provided with flutes parallel with its axis and the cutter is ata-ll times maintained at right angles with the gear axis, thereby dispensing with an angularly adjustable cutter.

bearing in the machine which has always `been' a detriment and also permitting 'of grinding the cutter upon its face without a specially designed grinding machine equipped for helicoidal grinding. Furthermore, when viewing the cutting faces ofthe teeth, along'a` flute 4in the direction of the 4o axis, they will 4not have awarpedappearance but'lwill' be perfectly radial," s11`bstan`* tially thesame as though each tooth was a single tool similar to that used i'n gear planing machines. 45

The result of these improvements in the Y cutter and' method is that the gear tooth Acurves 28 'andl aresymmetrical and each diametral plane the basic form of 4a system 5Mh of conjugate rolling curves is enveloped. 60.`

2.' A helicoid having surfaces .formed so that the projection, on a plane perpendicular to a chordal plane and parallel to a diametral Aplane of the portion of convoluvtions cut from said helicoid by said chordal *0.5 Y

plane will envelop the basic form of a systemvof conjugate rolling curves. 3. A helicoidal cutter having its cuttingteeth so shaped in a diametral plane that the projection of the cutting edges of all of the 70 teeth cut by a chordal plane, upon a plane perpendicular to said Chor-dal plane and parallel to said diametral plane will envelop the basic form required.

VILLIAM F. ZIMMERMANN.

l Witnesses: 4

B. E. BARNES, e A. C. BLAKEMAN. 

